Method and apparatus for transporting a client signal over an optical network

ABSTRACT

A method of transporting a client signal across an optical transport network (OTN) comprises dividing a received client signal into a plurality of parallel signals at a lower bit rate. The parallel signals are mapped into a respective number of optical data units (ODUs), each ODU having payload bytes and overhead bytes. Each ODU is mapped into a respective optical transport unit (OTUs) having payload bytes and overhead bytes. The OTUs are transmitted across respective optical carriers of a super-channel, the optical carriers of the super-channel being synchronously modulated. Optical channel control information is inserted into the overhead bytes of the ODU and/or OTU. The optical channel control information is used to manage and/or control the transport of the client signal using the super-channel.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a National stage of International Application No.PCT/EP2012/075110, filed Dec. 11, 2012, which claims priority to U.S.Patent Application No. 61/675,980, filed Jul. 26, 2012, which are herebyincorporated by reference.

TECHNICAL FIELD

This invention relates to optical transport networks and to methods andapparatus therefore.

BACKGROUND

Currently, the data traffic transported over the telecom opticaltransport networks is growing at a phenomenal pace and consequently thetransmitted bit rates over a single optical wavelength in a DWDMtransport systems are increasing rapidly. It is expected soon that thestandardized 100 Gb/s bit rate will not meet the need and a higherdigital rate is required.

Currently, transport equipment is designed with standardized interfacesand DWDM interfaces where multiple optical wavelengths are used totransport various digital bit rates. International TelecommunicationsUnion (ITU-T) Recommendation G.709 defines the optical transport network(OTN) interfaces and hierarchy. G.709 also defines the largest containerODU4 to transport 100 Gbit/s of data traffic.

Standards for the transport of data traffic greater than 100 Gbit/s, forexample 400 GBit/s or greater, are not yet defined.

SUMMARY

In one aspect there is provided a method of transporting a client signalacross an optical transport network (OTN), the method comprisingdividing a received client signal into a plurality of parallel signalsat a lower bit rate; mapping the parallel signals into a respectivenumber of optical data units (ODU) each having payload bytes andoverhead bytes; mapping each ODU into a respective optical transportunit (OTU) having payload bytes and overhead bytes; transmitting theOTUs across respective optical carriers of a super-channel, the opticalcarriers of the super-channel being synchronously modulated; andinserting optical channel control information (OCCI) into the overheadbytes of the ODU and/or OTU, the OCCI being used to manage and/orcontrol the transport of the client signal using the super-channel.

The use of super-channels together with in-band control and managementsignaling allows for increased transport capacity with minimummodifications to much existing transport equipment.

The OTN, ODU, OTU and the optical carriers of the super-channel may beconstructed according to ITU-T standard G.709. Other types of containers(ODU/OTU) are however contemplated.

The super-channel may be transmitted using a single laser. Thesuper-channel may consist of multiple frequency-locked carriers usingcoherent optical orthogonal frequency-division multiplexing (CO-OFDM),however other types of modulation may alternatively be used.

The OCCI may be used to identify which optical carriers are used tocarry the respective OTU, and may also include information aboutstructure, types, and management information about the signal/stransported.

The OCCI may be used to request a change in the optical carriers used totransport the client signal. This may include adding or subtractingsub-carriers, or re-allocating the same number of sub-carriers.

In a second aspect there is provided a method of transporting a clientsignal across an optical transport network (OTN), the method comprising:dividing a received client signal into a plurality of parallel signalsat a lower bit rate; mapping the parallel signals into a respectivenumber of optical data units (ODU) each having payload bytes andoverhead bytes; mapping each ODU into a respective optical transportunit (OTU) having payload bytes and overhead bytes; mapping theresulting OTUs into a higher bit rate OTU having payload bytes andoverhead bytes; transmitting the higher rate OTU across the OTN as anoptical super-carrier, the optical super-carrier having a wavelengthwider than the wavelength of an optical carrier normally allocated totransmitting a lower rate OTU across the OTN; inserting optical channelcontrol information (OCCI) into the overhead bytes of the ODU and/orOTU, the OCCI being used to manage and/or control the transport of theclient signal using the optical super-carrier.

The OTN, ODU, and OTU may operate according to G.709. The lower rate ODUand OTU may be ODU4 and OTU4 respectively, whilst the higher rate OTUmay be OTU5.

The lower bit rate OTU may first be interleaved to form a single higherbit rate signal for mapping into the higher bit rate OTU. Theinterleaving may be performed using bit, byte or block interleaving.Circuit processing may be used to de-skew/align the signals.

In an embodiment, the optical carriers have a wavelength defined in ITURecommendations G.694.1 and G.694.2 and the optical super-carrier has awavelength wider than what would be used for the optical carriers.

The use of super-carriers together with in-band control and managementsignaling allows for increased transport capacity without modificationsto much existing transport equipment.

In a third aspect there is provided a method of transporting a clientsignal across an optical transport network (OTN), the method comprising:dividing a received client signal into a plurality of parallel signalsat a lower bit rate; mapping the parallel signals into a respectivenumber of optical data units (ODU) each having payload bytes andoverhead bytes; mapping each ODU into a respective optical transportunit (OTU) having payload bytes and overhead bytes; transmitting theOTUs across respective optical carriers; inserting optical channelcontrol information (OCCI) into the overhead bytes of the ODU and/orOTU, the OCCI being used to request a change in the optical carriersused to transport the client signal.

The OTN, ODU, OTU may operate according to G.709. The optical carriersmay be formed as part of a super-channel or as standard parallelwavelengths as defined in G.709, G.694.1 and G.694.2.

The use of in-band signaling to change the number of optical carriersused to transport the client signal allows for increased flexibility forhandling the client signal.

There are also provided corresponding methods of receiving the opticalchannels and recovering the inserted OCCI. As noted, this may be used toassist in fully recovering all of the client signal, to manage thetransport network, to control changes in the number and/or assignment ofoptical carriers used for transport of the client signal.

These methods can occur at a client signal ingress and egress node, aswell as at intermediate nodes within the OTN.

There are also provided equipment such as optical nodes havingoptical-electrical-optical (OEO), optical-electrical (OE),electrical-optical (EO) capability which are arranged to carry out thesemethods. Similarly there are also provided computer code on a suitablecarrier and executable by a suitable processor to carry out the abovemethods.

The functionality described here can be implemented in hardware,software executed by a processing apparatus, or by a combination ofhardware and software. The processing apparatus can comprise a computer,a processor, a state machine, a logic array or any other suitableprocessing apparatus. The processing apparatus can be a general-purposeprocessor which executes software to cause the general-purpose processorto perform the required tasks, or the processing apparatus can bededicated to perform the required functions. Another aspect of theinvention provides machine-readable instructions (software) which, whenexecuted by a processor, perform any of the described methods. Themachine-readable instructions may be stored on an electronic memorydevice, hard disk, optical disk or other machine-readable storagemedium. The machine-readable medium can be a non-transitory medium. Themachine-readable instructions can be downloaded to the storage mediumvia a network connection.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will be described, by way of example only,with reference to the accompanying drawings in which:

FIG. 1 shows an Optical Transport Network (OTN);

FIGS. 2A and 2B show apparatus at a first node and a second node of FIG.1 where client traffic is carried using a super-channel;

FIG. 2C shows two examples of super-channel signals and a conventional100 G signal;

FIG. 3 shows an OTU frame structure;

FIG. 4 shows the overhead bytes of the OTU frame of FIG. 3;

FIG. 5 shows a method which can be performed at the first node of FIG.2A;

FIG. 6 shows a method of changing the optical channels structureaccording to an embodiment;

FIG. 7 shows a method which can be performed at the second node of FIG.2B;

FIGS. 8A and 8B show apparatus at a first node and a second node of FIG.1 where client traffic is carried using DWDM channels;

FIG. 9 shows a method which can be performed at the first node of FIG.8A;

FIG. 10 shows a method of implementing the change of optical channelsstructure;

FIG. 11 shows a method which can be performed at the second node of FIG.8B;

FIGS. 12A and 12B show apparatus at a first node and a second node ofFIG. 1 where client traffic is carried using a wide carrier, such as acarrier modulated with an ODU5/OTU5;

FIG. 13 shows a carrier for use in the embodiment of FIGS. 12A and 12B;

FIG. 14 shows a method which can be performed at the first node of FIG.12A;

FIG. 15 shows a method which can be performed at the second node of FIG.12B;

FIG. 16 shows processing apparatus for a computer-based implementation.

DETAILED DESCRIPTION

FIG. 1 shows an OTN network 10 and two nodes 11, 12 forming part of theOTN network 10 at which client signals can ingress 13 the OTN networkand/or egress 14 the OTN network 10.

FIGS. 2A and 2B show one embodiment of apparatus at the nodes 11, 12 ofFIG. 1 in more detail. FIG. 2A shows ingress functions at one of thenodes 11, 12. The node receives a 400 G client signal 13 and uses ademultiplexer/divider 21 to demultiplex/divide the client signal 13 intofour parallel 100 G signals 22 which are mapped by a mapper 23 into ODU4containers 24 as will be appreciated by those skilled in the art. Forsimplicity of explanation, not all steps of this process are described,however detailed explanations of these steps can be found in ITU-Tstandard G.709.

As will be appreciated by those skilled in the art, ODU4 containers 24are able to transport 100 G client signals across the OTN network 10,and thus the embodiment is able to transport the 400 G client signal 13across four parallel ODU4 signals. The ODU4 containers 24 are mapped bya further mapper 25 into OTU4 containers 26 as is known. A channelmanaging entity 31 inserts 32, 33 optical channel control informationinto the overhead bytes 24A, 26A of the ODU4 and/or OTU4 containers 24,26. The channel managing entity 31 may be implemented by a suitablyprogrammed processor and memory in the node 11, 12.

The set 28 of OTU4 signals are input to a super-channel multiplexer 29which cooperates with a super-transponder 30 to generate an opticalsignal 31 comprising a group of optical sub-carriers or channels totransport the OTU4 containers across the OTN 10. A super-channel cancomprise a group of optical carriers which are synchronously modulated.In this example, four sub-carriers or wavelengths are used whichcorrespond to the four parallel OTU4 streams. Various modulation schemesmay be used such as QAM, QPSK, 16QPSK, etc. The sub-carriers may befurther multiplexed to form part of a DWDM transport system.

The super-channel multiplexer 29 and super-channel transponder 30 can beimplemented in various ways as will be appreciated by those skilled inthe art. The Infinera DTN-X platform is a current commercially availableproduct.

In one implementation, the optical carriers are modulated synchronouslywhich provides improved optical performance. Such an implementation isdescribed in the paper “Terabit Superchannels for High SpectralEfficiency Transmission” by S. Chandrasekhar and Xiang Liu, in ECOC2010, 19-23 Sep., Torino Italy. The implementation described in thispaper uses coherent optical orthogonal frequency division multiplexing(CO-OFDM), however alternative super-channel implementations could alsobe used.

The super-channel mux 29 and super-transponders 30 effectively integratewhat would otherwise be the modulation of separate optical channels orwavelengths. The use of photonic integration has allowed theimplementation of super-channels or groups of multiple wavelengths to bemodulated together in a cost effective manner.

FIG. 2B shows apparatus at a node 11, 12 for egress of a client signal.A corresponding arrangement receives the four optical signals which formthe super-channel 79 and recovers 69 the 4x OTU4 streams 68, which aredemapped 65 into 4x ODU4 streams. A channel manager entity 71 recoversoptical channel control information 73, 72 from the overheads 66A, 64Aof the OTU4 and/or ODU4 66, 64. A transponder 70 receives the opticalsignal 79 which comprises the super-channel. A demultiplexer 69 recoversthe OTU4 streams 68. The OTU4 streams are demapped 65 to ODU4 streams64. A set 62 of output signals recovered from the ODU4s are combined 61and output as a client signal 14.

FIG. 2C shows two examples 96, 97 of 400 G super-channel signals and, byway of contrast, a conventional 100 G signal 95. The super-channelsignal 96 shown in FIG. 2C is of the type described above. It comprisesfour sub-carriers SC1, SC2, SC3, SC4. The super-channel signal 97comprises two sub-carriers SC1, SC2. As can be seen from these examples,the number of sub-carriers and the bandwidth of each sub-carrier canvary. Modulation scheme can be selected from a range of possiblemodulation schemes. A different modulation scheme may be used for one ormore of the sub-carriers in the plurality of sub-carriers.

In this embodiment, the number of sub-carriers of the super-channel andtheir particular wavelengths are referred to as the optical channelsstructure. The optical channel control information may include requeststo change the optical channels structure used to transport the clientsignal. For example, should the client wish to increase the clientsignal from 400 G to 500 G, this may be accommodated by adding a fifthparallel OTU4 signal and corresponding optical sub-carrier.Alternatively, it may be necessary to change which sub-carriers are used(without changing their number) due to operational networkconsiderations such as protection switching or congestion. In this caseone or more of the OTU4 streams may need to be switched to a differentoptical sub-carrier.

Management information relating to the optical channels structure iscommunicated between nodes using optical channel control information(OCCI) which is inserted into and recovered from the overhead bytes ofthe ODU and/or OTU containers as will be described in more detail below.This management information may include the number of optical carriersused in the super-channel, their identities and other managementinformation which would be familiar to those skilled in the art ofoptical transport network technologies. Alternatively or additionally,the OCCI may include requests, acknowledgements and other hand-shakingmessages in order to control a change in the optical channels structure,such as adding or subtracting optical carriers from the super-channel.

The optical channel control information (OCCI) may be distributed in theoverhead 24A, 26A of the ODU and OTU in any suitable manner. Theinformation may be in the overhead of just one of the parallel streamsof ODU/OTU or in any number of the parallel streams of ODU/OTN in anycombination of unique or redundant formats. FIG. 3 shows a standard OTUkframe structure which includes both OTUk OH (overhead) and ODUk OH asindicated. The client signal is mapped into the OPUk payload area asknown and as indicated in the figure. FIG. 4 shows the structure of theOH bytes 24A, 26A in more detail, where the acronyms represent:

-   -   ACT: Activation/deactivation control channel;    -   APS: Automatic Protection Switching coordination channel;    -   EXP: Experimental;    -   FAS: Frame Alignment Signal;    -   FTFL: Fault Type & Fault Location reporting channel;    -   GCC: General Communication Channel;    -   MFAS: MultiFrame Alignment Signal;    -   PCC: Protection Communication Control channel;    -   PJO: Positive Justification Opportunity;    -   PM: Path Monitoring;    -   PSI: Payload Structure Identifier;    -   RES: Reserved for future international standardisation;    -   SM: Section Monitoring;    -   TCM: Tandem Connection Monitoring.        In an example embodiment reserved bytes 9-14 in row 4 of the ODU        OH could be used, as could reserve bytes 13, 14 in row 1 of the        OTU OH. Other ODU and/or OTU OH bytes might also or        alternatively be used.

A method of transporting a client signal across an optical transportnetwork (OTN) is shown in FIG. 5. The method can be performed by one ofthe nodes 11, 12. Step 201 comprises dividing a received client signalinto a plurality of parallel signals at a lower bit rate. Step 202comprises mapping the parallel signals into a respective number ofoptical data units, ODU, each having payload bytes and overhead bytes.Step 203 comprises mapping each ODU into a respective optical transportunit, OTU, having payload bytes and overhead bytes. Step 204 comprisestransmitting the OTUs across respective optical carriers of asuper-channel, the optical carriers of the super-channel beingsynchronously modulated. Step 205 comprises inserting optical channelcontrol information into the overhead bytes of the ODU and/or OTU, theoptical channel control information being used to manage and/or controlthe transport of the client signal using the super-channel.

A method of implementing a change in the optical channels structure isillustrated in FIG. 6. A step 101 can monitor the client signal. Theclient may indicate a need for a higher (e.g. 500 G) or lower (e.g. 300G) rate signal, or the network may indicate a need to change theparticular optical wavelengths to be used for transport. Step 102determines if a change to the optical channel structure is needed. If aneed for such a change to the optical channels structure arises, thensuitable OCCI is inserted into the ODU/OTU OH 24A, 26A, 64A, 66A at step103. For example, if an additional wavelength is required to transportan increased bit rate 500 G client signal instead of the current 400 Gsignal, then predetermined “add wavelength” and “wavelength=21” typecommands can be inserted into byte 13 of row 1 of the OTU OH 26A, 66A,for example. The wavelength=21 will most likely correspond to awavelength adjacent the wavelengths transporting the current clientsignal, but need not be so limited. The method, which will beimplemented by the channel manager, then awaits an acknowledgement fromthe second node or receiver.

The second node recovers the OCCI, and if it can receive the suggestedoptical signal and accommodate the addition OTU4 stream, will provide apositive acknowledgement signal, again typically using the ODU/OTU OH ofoptical signals in the reverse direction.

Step 104 determines if an acknowledgement is received from the secondnode. Once the acknowledgement is received, the channel manager of thefirst egress node sends a control signal (34) to the demux 22 todemultiplex to five parallel 100 G streams which are then mapped intofive ODU4 and five OTU4. The channel manager 31 also controls 35 thesuper-channel mux 29 to generate a super-channel to accommodate the fiveOTU4 and controls 36 the super-transponder 30 to generate thecorresponding five sub-wavelength optical channels.

Various other dynamic control operations can be achieved in this way,for example to reduce the number of optical carriers used (if the clientsignal rate reduces for example) or to change which wavelengths areused. The OCCI channel may also be used to send other commands,acknowledgements or implement other control operations.

Similarly, various static control information can also be transferredacross the optical link for example confirming which optical channelsand modulation types are being used.

A method of receiving a signal from an optical transport network (OTN)is shown in FIG. 7. The method can be performed by one of the nodes 11,12. Step 211 comprises receiving optical carriers of a super-channel,the optical carriers of the super-channel being synchronously modulated.Step 212 comprises recovering optical transport units, OTU, each havingpayload bytes and overhead bytes. Step 213 comprises recovering opticaldata units, ODU, each having payload bytes and overhead bytes. Step 214comprises recovering a plurality of parallel data signals from the ODUs.Step 215 comprises combining the plurality of parallel data signals intoa client signal at a higher bit rate. Step 216 comprises recoveringoptical channel control information from the overhead bytes of the ODUand/or OTU, the optical channel control information being used to manageand/or control the transport of the client signal using thesuper-channel.

FIGS. 8A and 8B show an alternative embodiment which does not usesuper-channels but utilises the standard OTN/DWDM system of opticalchannels which are modulated separately (e.g. using OCh4) and thenoptically multiplexed to generate a DWDM signal. The initial stages ofthis embodiment are the same as described for the previous embodiment,and common reference numerals are used to indicate similar features. Inthis arrangement, each OTU4 is mapped into a respective OCh4 which isused to modulate 41 a respective separate laser. Four parallel opticalwavelengths 42 are then used to transport the client signal across tothe egress node. The process including the demux/divide 22 is stillcontrolled by the channel manager entity 31 which inserts OCCI into theODU and/or OTU OH 24A, 26A. FIG. 8B shows apparatus at a second node 12which receives the optical signal. In a corresponding manner, the secondnode 12 receives the four optical wavelengths 82 and recovers the fourparallel OTU4 streams according to the G.709 standard. These containersare demapped into four ODU4 64 which are fed to the mux/combiner 61 toreconstitute the client signal 14. Any de-skewing processing can also becarried out. The channel manager 71 of the second node 12 recovers 72,73, the OCCI from the ODU/OTU OH 64A, 66A.

FIG. 9 shows a method of transporting a client signal across an opticaltransport network (OTN), which can be performed by one of the nodes 11,12. Step 301 comprises dividing a received client signal into aplurality of parallel signals at a lower bit rate. Step 302 comprisesmapping the parallel signals into a respective number of optical dataunits, ODU, each having payload bytes and overhead bytes. Step 303comprises mapping each ODU into a respective optical transport unit,OTU, having payload bytes and overhead bytes. Step 304 comprisestransmitting the OTUs across respective optical carriers. Step 305comprises inserting optical channel control information into theoverhead bytes of the ODU and/or OTU, the optical channel controlinformation being used to request a change in the optical carriers usedto transport the client signal.

FIG. 10 shows a method of implementing changes to the optical channelsstructure, whether these are implemented using the super-channelembodiment or the separate optical channels DWDM embodiment. In thisparticular example a request to increase the client signal transportfrom 500 G to 700 G is received at step 111. However, many alternativerequests could also be accommodated as would be appreciated by thoseskilled in the art. The method can be implemented by the channel managerentity, which may receive the request upon completion of the method ofFIG. 6, for example. At step 112 the channel manager 31 instructs thedemux/divider to split the incoming client signal into seven parallelstreams of 100 G and to map these into seven ODU4 streams. At step 113the method adjusts the OCCI input into the ODU/OTU OH. For example, theOCCI can indicate which optical channels are being used and in whichorder so that the client signal can be correctly reconstituted. At steps115, 116 the method then reconfigures the super-channel mux andsuper-transponder as appropriate. Alternatively, if a standard DWDMoptical system is used, at step 114 the method maps seven OTU4 aremapped to seven OCh4 which are used to modulate seven separatewavelength lasers, as is known.

Alternatively, at step 117 the OCCI may be forwarded using control planeor management plane messaging in an out-of-band signal. At steps 119,120 the method then reconfigures the super-channel mux andsuper-transponder as appropriate. Alternatively, if a standard DWDMoptical system is used, at step 118 the method maps seven OTU4 aremapped to seven OCh4 which are used to modulate seven separatewavelength lasers.

A method of receiving a signal from an optical transport network (OTN)is shown in FIG. 11. The method can be performed by one of the nodes 11,12. Step 311 comprises receiving optical carriers. Step 312 comprisesrecovering optical transport units, OTU, each having payload bytes andoverhead bytes. Step 313 comprises recovering optical data units, ODU,each having payload bytes and overhead bytes and can also includeperforming de-skewing. Step 314 comprises recovering a plurality ofparallel data signals from the ODUs. Step 315 comprises combining theplurality of parallel data signals into a client signal at a higher bitrate. Step 316 comprises recovering optical channel control informationfrom the overhead bytes of the ODU and/or OTU, the optical channelcontrol information being used to manage and/or control the transport ofthe client signal using the super-channel.

Whilst various examples have been given, the invention is not solimited. For example any number of optical channels may be used, notjust four optical channels for a 400 G client signal. SimilarlyODU3/OTU3, ODU5/OTU5 or other variations of OTN containers couldalternatively be used.

A further alternative embodiment is shown in FIGS. 12A and 12B, whichutilises OTU5 containers from recent developments in the ITU-T G.709standard. OTU5 are the next higher rate transport container for OTN asdefined by G.709. Whilst the exact definition of the data rate to beused by ODU5 is still to be agreed, this will be significantly higherthan the current highest OTU4 container which can support 100 G clientsignals over a single optical carrier. It is anticipated that ODU5 willsupport either 400 G or 1T (1000 G) client signals and will be capableof carrying multiple ODU4 containers. The current G.709 living list(Version 2011-05) is available from ITU-T and details the currentspecification options for ODU5 in more detail. However these will followthe G.709 principles for earlier defined data rates so that the skilledperson will be fully understanding of the use of ODU5 as described inthis embodiment.

In a similar manner to the embodiments of FIGS. 2A, 2B and 8A, 8B, theincoming client signal 13 is divided 21 into four parallel digitalsignals 22 which are mapped 23 into four ODU4 containers 24. These ODU4are then mapped 25 into OTU4 containers 26 according to G.709. Thechannel manager entity 31 inserts OCCI into the overheads 24A, 26A ofthe ODU4 and/or OTU4 as previously described. The four OTU4 are theninput to an interleaver 45 which bit, byte or block interleaves the fourparallel OTU4 signals into a single digital stream 46 which is thenmapped 48 into the payload bytes of an OTU5 container 47. As per G.709,overhead bytes 47A are added. The OTU5 container 47 shown corresponds toa 400 G data rate, however other container sizes could alternatively beused with the number of OTU4 containers added adjusted accordingly aswould be appreciated by those skilled in the art. The OTU5 are thenfurther processed according to G.709 in a manner corresponding to howolder OTU containers are processed (e.g. OTU4, OTU3 etc.)—for exampleprocessing into OCh5. The OTU5 containers are applied to a super-carriertransponder which generates a wide bandwidth optical carrier modulatedby the OTU5 data. As will be appreciated, a wider bandwidth opticalsignal allows a higher data rate signal to be transported using the samemodulation rate and type.

FIG. 12B shows apparatus at one of the nodes 11, 12 which receives theoptical signal 90 at a transponder/receiver 89 and recovers the higherrate (e.g. OTU5) container. A bitstream 86 is recovered from thehigher-rate containers 87 and the bitstream is de-interleaved 85 to aparallel set of lower-rate OTUs (e.g. OTU4). These containers aredemapped 65 into four ODU4 which are fed to the mux/combiner 61 toreconstitute the client signal 14. The channel manager 71 of the secondnode 12 recovers 72, 73, 77 the OCCI from one or more of the ODU/OTU OH64A, 66A, 87A.

FIG. 13 shows a wide bandwidth optical carrier 50, 90 which can be usedto carry the higher data rate signal, such as an OTU5, and aconventional, narrower bandwidth, optical carrier 140 which can be usedto carry a lower rate signal. As an example, a conventional 100 G signalcan have a bandwidth of 50 GHz while the higher rate signal can have abandwidth of 75 GHz, although other carrier bandwidths can be used.

G.709 is associated with a grid of optical wavelengths which are used tocarry ODU4 signals. This grid is defined in ITU-T G.694 and specifiesthe frequency grid, anchored to 193.1 THz. This supports a variety ofchannel spacings ranging from 12.5 GHz to 100 GHz. The wavelengths ofthe optical carriers fit within these spacings. The super-carrier has awavelength broader than what would be used for the optical carriers andspans multiple defined spacings.

Using a super-carrier with a wavelength wider than the optical carrierwavelengths provides an alternative to using higher order modulationand/or higher optical bit rates to carry higher data rate signals likeOTU5. This eases the requirements on optical components making themcheaper to implement. The super-carrier can co-exist with conventionalcarriers in the OTN 10.

The super-carrier is received by a super-carrier transponder at theegress node and the OTU5 recovered using known G.709 technology. TheOTU5 payload is de-interleaved to recover the original parallel OTU4signals. These are de-mapped into 4 ODU4 signals which are combined togenerate the original 400 G client signal. Signal processing andde-skewing/alignment of the individual signals are performed asnecessary.

Meanwhile, the egress node's channel manager entity recovers OCCI fromthe overheads of the OTU and/or ODU as previously described. This allowsfor management as well as control of the super-carrier—for example tochange the wavelength to accommodate a different size client signal.

As with the other embodiments, the specific examples given are notlimiting, and could be altered—for example ten interleaved OTU4 could bemapped into a suitably sized OTU5.

FIG. 14 shows a method of transporting a client signal across an opticaltransport network (OTN) which can be performed by one of the nodes 11,12. Step 401 comprises dividing a received client signal into aplurality of parallel signals at a lower bit rate. Step 402 comprisesmapping the parallel signals into a respective number of optical dataunits, ODU, each having payload bytes and overhead bytes. Step 403comprises mapping each ODU into a respective optical transport unit,OTU, having payload bytes and overhead bytes. Step 404 comprises mappingthe resulting OTUs into a higher bit rate OTU having payload bytes andoverhead bytes. Step 405 comprises transmitting the higher rate OTUacross the OTN as an optical super-carrier, the optical super-carrierhaving a bandwidth wider than the bandwidth of an optical carriernormally allocated to transmitting a lower rate OTU across the OTN. Step406 comprises inserting optical channel control information into theoverhead bytes of the ODU and/or OTU, the optical channel controlinformation being used to manage and/or control the transport of theclient signal using the optical super-carrier.

A method of receiving a signal from an optical transport network (OTN)is shown in FIG. 15. The method can be performed by one of the nodes 11,12. Step 411 comprises receiving an optical super-carrier having abandwidth wider than a bandwidth of an optical carrier normallyallocated to transmitting a lower rate OTU across the OTN. Step 412comprises recovering higher-rate optical transport units, OTU, eachhaving payload bytes and overhead bytes. Step 413 comprises recoveringlower-rate optical transport units, OTU, each having payload bytes andoverhead bytes. Step 414 comprises recovering optical data units, ODU,each having payload bytes and overhead bytes. Step 415 comprisesrecovering a plurality of parallel data signals from the ODUs. Step 416comprises combining the plurality of parallel data signals into a clientsignal at a higher bit rate and performing any de-skewing processing, ifrequired. Step 417 comprises recovering optical channel controlinformation from the overhead bytes of the ODU and/or OTU, the opticalchannel control information being used to manage and/or control thetransport of the client signal using the optical super-carrier.

FIG. 16 shows an exemplary processing apparatus 130 which may beimplemented as any form of a computing and/or electronic device, and inwhich embodiments of the system and methods described above may beimplemented. Processing apparatus 130 can be provided at one of thenodes 11, 12. Processing apparatus may implement any of the methodsdescribed above. Processing apparatus 130 comprises one or moreprocessors 131 which may be microprocessors, controllers or any othersuitable type of processors for executing instructions to control theoperation of the device. The processor 131 is connected to othercomponents of the device via one or more buses 136. Processor-executableinstructions 133 may be provided using any computer-readable media, suchas memory 132. The processor-executable instructions 133 can compriseinstructions for implementing the functionality of the describedmethods. The memory 132 is of any suitable type such as read-only memory(ROM), random access memory (RAM), a storage device of any type such asa magnetic or optical storage device. Additional memory 134 can beprovided to store data 135 used by the processor 131. The processingapparatus 130 comprises one or more network interfaces 138 forinterfacing with other network entities, such as other nodes 11, 12 ofthe network 10.

Modifications and other embodiments of the disclosed invention will cometo mind to one skilled in the art having the benefit of the teachingspresented in the foregoing descriptions and the associated drawings.Therefore, it is to be understood that the invention is not to belimited to the specific embodiments disclosed and that modifications andother embodiments are intended to be included within the scope of thisdisclosure. Although specific terms may be employed herein, they areused in a generic and descriptive sense only and not for purposes oflimitation.

The invention claimed is:
 1. A method of transporting a client signalacross an optical transport network, the method comprising: dividing areceived client signal into a plurality of parallel signals at a lowerbit rate; mapping the parallel signals into a respective number ofoptical data units (ODUs), each ODU having payload bytes and overheadbytes; mapping each ODU into a respective optical transport unit (OTU)having payload bytes and overhead bytes; transmitting the OTUs acrossrespective optical carriers of a super-channel, the optical carriers ofthe super-channel being synchronously modulated; and inserting opticalchannel control information into the overhead bytes of the ODU and/orOTU, the optical channel control information being used to manage and/orcontrol the transport of the client signal using the super-channel,wherein the optical channel control information in the overhead bytes ofthe ODU and/or OTU includes a request of change of the synchronouslymodulated optical carriers of the super-channel.
 2. The method accordingto claim 1, wherein the optical carriers of the super-channel areconstructed according to ITU-T standard G.709.
 3. The method accordingto claim 1, wherein the super-channel is transmitted using a singlelaser.
 4. The method according to claim 3, wherein the super-channelcomprises multiple frequency-locked carriers using coherent opticalorthogonal frequency-division multiplexing (CO-OFDM).
 5. The methodaccording to claim 1, wherein the optical channel control informationidentifies at least one of: which optical carriers are used to carry therespective OTU, information about structure, information aboutmodulation type, and management information about the signalstransported.
 6. The method according to claim 1, wherein the changecomprises at least one of: adding sub-carriers, subtractingsub-carriers, and re-allocating the same number of sub-carriers.
 7. Themethod according to claim 1, further comprising controlling at least oneof the steps of: the dividing the received client signal into theplurality of parallel signals, the mapping the plurality of parallelsignals into the respective number of ODUs, the mapping each ODU intothe respective OTU and the transmitting the OTU across respectiveoptical carriers of a super-channel.
 8. The method according to claim 7,wherein the at least one of the steps controlled are performed uponreceiving an acknowledgement from a node.
 9. A method of receiving asignal from an optical transport network, the method comprising:receiving optical carriers of a super-channel, the optical carriers ofthe super-channel being synchronously modulated; recovering opticaltransport units (OTUs), each OTU having payload bytes and overheadbytes; recovering optical data units (ODUs), each ODU having payloadbytes and overhead bytes; recovering a plurality of parallel datasignals from the ODUs; combining the plurality of parallel data signalsinto a client signal at a higher bit rate; and recovering opticalchannel control information from the overhead bytes of the ODU and/orOTU, the optical channel control information being used to manage and/orcontrol the transport of the client signal using the super-channel,wherein the optical channel control information in the overhead bytes ofthe ODU and/or OTU includes a request of change of the synchronouslymodulated optical carriers of the super-channel.
 10. An apparatus foruse at a node for transporting a client signal across an opticaltransport network comprising: a demultiplexer arranged to divide areceived client signal into a plurality of parallel signals at a lowerbit rate; an optical data unit (ODU) mapper arranged to map the parallelsignals into a respective number of ODUs, each ODU having payload bytesand overhead bytes; an optical transport unit (OTU) mapper arranged tomap each ODU into a respective OTU having payload bytes and overheadbytes; a transponder arranged to transmit the OTUs across respectiveoptical carriers of a super-channel, the optical carriers of thesuper-channel being synchronously modulated; and a channel managerarranged to insert optical channel control information into the overheadbytes of the ODU and/or OTU, the optical channel control informationbeing used to manage and/or control the transport of the client signalusing the super-channel, wherein the optical channel control informationin the overhead bytes of the ODU and/or OTU includes a request of changeof the synchronously modulated optical carriers of the super-channel.11. An apparatus for use at a node for receiving a signal from anoptical transport network comprising: a receiver arranged to receiveoptical carriers of a super-channel, the optical carriers of thesuper-channel being synchronously modulated; a demultiplexer arranged torecover optical transport units (OTUs), each OTU having payload bytesand overhead bytes; an OTU de-mapper arranged to recover optical dataunits (ODUs), each ODU having payload bytes and overhead bytes from theOTUs; an ODU de-mapper arranged to recover a plurality of parallel datasignals from the ODUs; a multiplexer arranged to combine the pluralityof parallel data signals into a client signal at a higher bit rate; anda channel manager arranged to recover optical channel controlinformation from the overhead bytes of the ODU and/or OTU, the opticalchannel control information being used to manage and/or control thetransport of the client signal using the super-channel, wherein theoptical channel control information in the overhead bytes of the ODUand/or OTU includes a request of change of the synchronously modulatedoptical carriers of the super-channel.
 12. A method of transporting aclient signal across an optical transport network in a first node, themethod comprising: dividing a received client signal into a plurality ofparallel signals at a lower bit rate; mapping the parallel signals intoa respective number of optical data units (ODUs), each ODU havingpayload bytes and overhead bytes; mapping each ODU into a respectiveoptical transport unit (OTU) having payload bytes and overhead bytes;transmitting the OTUs across respective optical carriers of asuper-channel, the optical carriers of the super-channel beingsynchronously modulated; and inserting optical channel controlinformation into the overhead bytes of the ODU and/or OTU, the opticalchannel control information being used to manage and/or control thetransport of the client signal using the super-channel, wherein theoptical channel control information in the overhead bytes of the ODUand/or OTU includes a request to increase a number of the opticalcarriers of the super-channel.
 13. The method according to claim 12,wherein the optical channel control information is received by a secondnode, wherein the second node provides a positive acknowledgement to thefirst node up determining the second node can accommodate the requestedincrease of the number of the optical carriers of the super-channel. 14.The method according to claim 13, further comprising: upon receiving thepositive acknowledgement at the first node, dividing the received clientsignal into the increased number of parallel signals; mapping theparallel signals into the increased number of optical data units (ODUs),each ODU having payload bytes and overhead bytes; mapping each ODU intoa respective optical transport unit (OTU) having payload bytes andoverhead bytes; and transmitting the OTUs across respective opticalcarriers of the super-channel, the optical carriers of the super-channelbeing synchronously modulated, wherein the number of the opticalcarriers is the increased number.